At a military training centre some 60 kilometres (40 miles) north of Kiev, Karpunets, 40, and some 5,000 other recruits are being put through their paces.
Vitaliy Karpunets crawls under barbed wire before jumping over a smoking bonfire into a trench as he fires off his Kalashnikov at an imaginary enemy.
The men are part of the latest wave of mobilisation that Ukraine is carrying out, calling up some 100,000 men to bolster its struggling armed forces locked in a 10-month conflict with pro-Russian rebels in the east.
Karpunets, who did his compulsory military service in the early 1990s, is one of roughly 4,000 who signed up voluntarily.
He left his wife and two-year-old daughter at home convinced that he needed to enlist to fight an insurgency that Kiev says is armed by Moscow and often made up of regular Russian troops.
"You need to be a man and fight back the enemy if needs be," Karpunets, his face black with soot and breathing heavily, tells AFP.
For the vast majority of those now entering the army the decision was made for them when they received their call-up papers.
Senior Ukrainian official Oleksiy Pokotylo says that since the fresh draft -- the fourth wave so far -- began in mid-January some 105,000 men with military experience have been sent summons.
Of them, he says, some 70,000, or roughly 66 percent, have headed to their local recruitment office and over 22,000 are already undergoing training.
'Only idiots aren't scared'
Taxi driver Sergiy Prokopchuk says there were no second thoughts about answering the call but admits that the idea he could be on the frontline is a few weeks is scary.
"Only an idiot isn't afraid," the well-built 30-year-old says.
"But the brave must overcome their fear and go to defend their motherland."
Ukraine's President Petro Poroshenko said on February 9 that 1,432 troops have been killed since April. Some of the fiercest fighting has raged since he announced that toll.
Faced with the danger, reactions to the latest call-up have by no means been unanimous.
Earlier this month, Ukrainian authorities in the western region of Ivano-Frankivsk arrested journalist Ruslan Kotsaba on suspicion of treason after he posted a video online urging people to dodge the draft.
"I would prefer to go to prison than to participate in this fratricidal war," Kotsaba said in the footage, which was viewed more than 300,000 times.
"I refuse to be drafted and call on everyone who is called up to refuse," he said in the video posted January 17.
Kotsaba was ordered held in jail for 60 days as the security services probed the allegations. He faces up to 15 years in prison if convicted.
But among those undergoing training ahead of a possible deployment to the east there appeared to be no such doubts.
Oleksandr Grabovsky's wife saw him off with tears in her eyes when he left for training two weeks ago.
The newly-enlisted soldier, who has been assigned to a mechanised division, is now trying to forget the emotion of parting and focus on preparing for the war.
"They're feeding us well and we've got everything we need for our training," Grabovsky says.
Grabovsky did his military service only a few years back and said he now felt he owed it to his country to serve.
"If you've got to go to defend your homeland, then you've got to go," he said.
By Dmytro Gorshkov (AFP)